Inulinase production from <i>Aspergillus oryzae</i> OY-3 using onion peel as an alternative, low-cost substrate

Inulinases have broad biotechnological applications in diverse industrial sectors such as the food, confectionary, pharmaceutical, and biofuel industries. This study was aimed at the production of inulinase from a filamentous fungus, under submerged fermentation conditions, using onion peel as a cheap, and renewable substrate. Nine strains of fungi were isolated from the soil of a Sugarcane Farmland in Obafemi Awolowo University, Ile-Ife, Nigeria, and screened for their relative inulinase production. The identity of the selected inulinase-producing fungus was presumptively determined by phenotypic method, and this was confirmed by molecular method through the sequencing of the internal transcribed spacer region of the ribosomal DNA. The agro-wastes onion, orange, pineapple, and plantain peels were collected from the Fruit Market and processing sites in Ile-Ife, Nigeria, and screened as suitable substrates for inulinase production from the selected fungus. The proximate analysis of the selected onion peel was carried out. The effect of each of the fermentation parameters incubation period, carbon sources, nitrogen sources, inoculum size, pH, and temperature on the enzyme production was also studied. The identity of the selected inulinase-producing fungus was confirmed by molecular method as Aspergillus oryzae OY-3. Of the agro-wastes screened, onion peel was observed to be the best substrate for the enzyme production from the fungus. The cultural parameters eliciting optimum inulinase production from the fungus were an incubation period of 72 h, initial pH, and incubation temperature of 4.0 and 30oC, respectively. Others were a fungal spore inoculum size 0.5 mL, onion peel concentration 2.0%w/v , and nitrogen source peptone. This study has revealed the feasibility of the production of the industrially-important inulinase from A. oryzae OY-3, isolated from the soil of a Sugarcane Farmland, using onion peel as a low-cost, alternative substrate.